1. Field of the Invention
The present invention relates, in general, to a rotor having an embedded permanent magnet, and more particularly, to a structure comprising a permanent magnet suitable for a rotor core preferably having a thin, circular, hollow section and a structure which suitably reduces the amount of permanent magnet.
2. Description of the Related Art
Generally, a synchronous motor using a permanent magnet (or a magnet) preferably includes a surface permanent magnet (SPM) type motor in which a permanent magnet is suitably attached onto the surface of a rotor, and an interior permanent magnet (IPM) type motor in which a permanent magnet is suitably embedded into a core of a rotor. The IPM type motor is generally used because the SPM type motor has a complicated structure for preventing the magnet from being scattered at fast rotation speeds whereas the IPM type motor has a relatively simple structure. Preferably, the IPM type motor is also used as a motor for driving a hybrid car.
Japanese Unexamined Patent Publication No. 2000-316241, incorporated by reference in its entirety herein, discloses an example of an IPM motor in which a pole of a rotor is preferably composed of magnets having a two-stage, 3-divided, substantially U-shaped arrangement. Japanese Unexamined Patent Publication No. 2004-88846, incorporated by reference in its entirety herein, discloses another example of an IPM motor in which a pole of a rotor is preferably composed of magnets having a single-stage, 3-divided, substantially U-shaped arrangement. Preferably, the net torque for rotating an IPM motor is suitably expressed as the sum of attractive (or repulsive) magnetic torque between embedded magnets and an electromagnet of a coil as a pole of a stator and magneto-resistance torque generated, owing to a difference between dielectric coefficients of magnets and a metallic section such as a silicon steel plate in a pole of a rotor.
IPM motors as described in the art can obtain suitably high torque owing to a substantially U-shaped arrangement of the magnets, but the diameter of the rotor needs to be suitably increased making it difficult to make them compact.
Further, a motor for a hybrid car requires a structure for assembling a connection mechanism to a crank shaft or a transmission, i.e. an existing mass-produced driving system. Accordingly, the rotor core thereof has a circular hollow section with the center being largely empty and thus a conventional V or U shaped arrangement of permanent magnets cannot be suitably obtained. Therefore, an arrangement of magnets for high performance and efficiency is suitably required.
Further, since a rare metal such as niobium as a high coercive magnet is expensive, in order to reduce costs, a structure for reducing the amount of magnets to be used is also required.
The above information disclosed in this the Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.